In general, the invention relates to the treatment of an aqueous effluent, comprising one or more dissolved gaseous compounds, for example carbon dioxide and/or nitrogen, in order to separate therefrom all or part of said compounds, considered for example as pollutants, in order to obtain a treated aqueous phase, depleted of said gas compound(s), or in any case whereof the concentration of said compounds is thereby monitored or controlled, for example below or above a predefined threshold.
More particularly, but by way of example, the treatment considered by the present invention forms part of any method for culturing a living organism, for example aquaculture, in recirculated aqueous medium, according to which in general:                a bath of the aqueous medium is provided, uncovered or not, broken down or not into elementary circuits in series or in parallel, in which the cultured living organism, for example fish, is immersed,        an effluent stream, from which the aqueous effluent to be treated is obtained, is tapped off from the bath, to control the concentration of dissolved gaseous compounds in said aqueous effluent,        a feed stream, obtained from the treated aqueous phase, that is, depleted of dissolved gaseous compounds, is supplied to or reinjected into the same bath.        
In the context of the present invention, “living organism” means living organisms of the lower kingdom, such as microorganisms, algae, etc., and also living organisms of the higher kingdom, such as fish, molluscs or shellfish.
For the purposes of the description of the present invention, said invention is now introduced, clarified and commented on with reference to aquaculture in recirculated aqueous medium.
Under the conditions of aquaculture in recirculated aqueous medium, to promote the growth and health of the fish, it is known today that it is essential to control the dissolved gas concentration, that is, to maintain:                dissolved oxygen below a certain threshold,        the dissolved carbon dioxide and nitrogen.        
To also deplete the aquaculture aqueous effluent of at least one dissolved gaseous compound, for example dissolved carbon dioxide, a column called a ventilated column is used, essentially consisting of a column filled with a packing consisting of discrete elements favoring a gas/liquid interface (or diopter) with a large developed surface area according to the cross section and height of the column. The offgas to be treated is introduced and distributed at the top of the column, above the packing, for example by sprinkling, while an elution or “stripping” gas phase, less rich in said gaseous compound (carbon dioxide) than the aqueous effluent, for example pressurized air, is introduced at the bottom of the column, for example into the packing. A liquid stream constituting the treated aqueous phase is extracted at the bottom of the column, and an offgas stream, enriched with said dissolved gaseous compound, is extracted at the top of the column.
In the context of the present invention, the expression “less rich in said gaseous compound” means, all other things remaining equal (including pressure), the concentration of said gaseous compound in the aqueous phase that would be in equilibrium with the concentration of said gaseous compound in the gas phase is lower than the effective concentration of said gaseous compound in the treated aqueous phase. Essentially, using a ventilated column is equivalent to circulating water through a gas phase, in this case air, roughly in the ratio of 10 volumes of air in countercurrent flow to one volume of treated water.
The implementation of these ventilated columns, which can be treated as air-cooled cooling towers, has many drawbacks.
Their dissolved gas extraction efficiency is limited. For carbon dioxide for example, it appears impossible to extract more than 25 to 30% of the dissolved carbon dioxide. This is due to the limited developed surface area of the gas/liquid interface, which is further decreased by the development of biofilms in the column packing, on the one hand, and by clogging and preferential paths for the water in the packing, on the other.
Any ventilated column also consumes a relatively large amount of energy, due to its operation, in particular because the aqueous effluent to be treated must be pumped to send it to the top of the column.
With regard to maintaining the temperature of the outgoing treated aqueous phase, compared with the incoming aqueous effluent, which may be important in an aquaculture method in recirculated aqueous medium, the implementation of a ventilated column inherently dissipates heat energy, making it necessary in certain cases to heat the treated aqueous phase at the outlet of the ventilated column.
Any ventilated column represents a chamber with a non-negligible volume, given the volume of air (circulating gas phase), which gives rise to a relatively bulky installation, possibly representing a non-negligible investment in material and infrastructure.
And, from the standpoint of biological safety, like the air-cooled cooling towers, the implementation of a ventilated column may generate aerosols liable to come into contact with the surrounding atmosphere, in view of the overpressure existing in the ventilated column.
It is an object of the present invention to remedy the abovementioned drawbacks of ventilated columns.